Electric switch with frangible and expendable electrodes



30, 1966 L. L. ALSTON ETAL 3,

ELECTRIC SWITCH WITH FRANGIBLE AND EXPENDABLE ELECTRODES Filed 001;. 14, 1964 2 Sheets-Sheet 1 FIG. 1. [7

g- 1956 L. ALSTON ETAL 3,269,937

ELECTRIC SWITCH WITH FRANGIBLE AND EXPENDABLE ELECTRODES Filed Oct. 14, 1964 2 Sheets-Sheet 2 United- States Patent 3,269,987 ELECTRIC SWITCH WITH FRANGIBLE AND EXPENDABLE ELECTRODES Liviu Leonard Alston, Abingdon, and Patrick Joseph Rogers, Oxford, England, assignors to United Kingdom Atomic Energy Authority, London, England Filed Oct. 14, 1964, Ser. No. 403,891 Claims priority, application Great Britain, Oct. 17, 1963, 41,035/63; June 9, 1964, 23,794/ 64 Claims. (Cl. 200-61.08)

This invention relates to electric switches which are made to close mechanically.

In the development of clampswitches for nuclear fusion experiments a need has arisen for a switch which is able to hold off 40 kilovolts until the instruction is given for it to close. When closed the switch must have a very low resistance, a low inductance, and be able to carry 100 kiloamps and at lea-st some hundreds of coulornb s. It is required that the switch close in a time of the order of 100 microseconds from the instant of giving the instruction. The jitter, that is the variation in the time taken to close, must be small.

Hitherto no mechanical switch has met these requirements, and it is an object of the present invention to provide a mechanical switch which is capable of doing so.

According to the present invention, an electric switch comprises a layer of electrically-insulating material sandwiched between two expendable electrodes, two main electrodes between which the sandwich is held such that the two main electrodes contact the two expendable electrodes respectively, the electric supply to be switched being arranged to be connected across the main electrodes, a pair of aligned aperture-s in the main electrodes normal to the general plane of the sandwich, a plunger, and means operated when the switch is to be closed to force the plunger into the apertures such that the sandwich is pierced and deformed portions of the expendable electrode first pierced contact the other expendable electrode and complete the electric path between the main electrodes.

Preferably each expendable electrode is formed by a metallic layer, the expendable electrode first pierced by the plunger being formed of a relatively soft and ductile metal and the other expendable electrode being formed of a relatively hard met-a1. Preferable the expendable electrodes are formed of soft annealed copper and hard rolled copper respectively.

A switch in accordance with the present invention will now be described by way of example with reference to the accompanying drawing, in which:

FIGURE 1 shows the essential parts of the switch diagrarnmatically,

FIGURE 2 shows an enlarged detail of part of the switch after closure,

FIGURE 3 shows a modification to a part of the switch and FIGURE 4 shows another modification to a part of the switch.

Referring now to FIGURE 1 of the drawing, the switch includes a pair of main electrodes 1 and 2, between which is positioned a sandwich 3 comprising a polythene layer 4 between copper layers Sand 6 which (form expendable electrodes. The layer 5 is formed of soft annealed copper and the layer 6 is formed of hard rolled copper.

The main electrodes 1 and 2 have aligned apertures 7 and 8, respectively, into which a plunger 9 is forced when the switch is to be closed. The inner edge of the main electrode 1 has a hard steel insert 10 on the side nearer the plunger 9.

The plunger 9 has a hollow, tapered tip 11 of steel at 3,269,987 Patented August 30, 1966 ice the end which is to pierce the sandwich 3. The remainder of the plunger 9 is of duralumin and consists of a hollow shaft 12 and a disc 13. The plunger 9 is movable axially on a brass guide 14 carried on an insulating rod 15, and in the rest position shown has the disc 13 adjacent a resin-encapsulated coil 16.

In one embodiment of the switch the apertures 7 and I 8 each have a diameter of 1.025 inches, the plunger 9 has a diameter of 0.980 inch, and the tip 11 is tapered at an angle of 20 to the axis of the plunger 9 for a distance of 0.125 inch from the end.

One end of the coil 16 is earthed and the other end is connected by way of a very fast, electronic, subsidiary svgitch 17, such as a trigatron, to an energising capacitor 1 The operation is as follows. The electric supply to be switched is connected across the main electrodes 1 and 2 which, with the switch open, are insulated from one another by the polythene layer 4. The capacitor 18 is charged to a suitable potential, which in the embodiment mentioned is 8 kilovolts.

When the switch is to be closed, the subsidiary switch 17 is closed so causing the capacitor 18 to discharge through .the coil 16. The rapidly rising current in the coil 16 induces an oppositely sensed current in the disc 13 and this results in the plunger 9 being forced into the apertures 7 and 8, so that the tip 11 pierces the sandwich 3. This causes a section of the polythene 4 and the layer 6 (which is hard) to be punched out. The appropriate part of the layer 5 (which is soft and ductile) is however extruded to contact the layer 6 to which it may become welded due to the current which then flows between the main electrodes 1 and 2 via the layers 5 and 6.

This extrusion, which is illustrated in FIGURE 2, is such that the plunger 9 is protected from damage by areing as any contact burning which occurs is largely confined to the layers 5 and 6.

To reopen the switch the plunger 9 is withdrawn and a fresh sandwich 3 is substituted ready for the next closure. This substitution can be arranged to be done automatically.

In the embodiment mentioned the layer 5 is 0.02 inch thick and the layer 6 is 0.01 inch thick. The polythene 4 is 0.02 inch thick which enables the switch to hold olf 40 kilovolts and to be closed in 40 microseconds. When closed the switch has a resistance of a few microhms.

Referring now to FIGURE 3, the steel insert 10 (FIG- URE 1) may be replaced by a very hard sintered aluminium oxide insert 19 having an aperture 20 which is aligned with the aperture 8 (FIGURE 1). The insert 19 is tapered so that the annular surface which bears on the layer 6 is very narrow. To hold the insert 19 in place the main electrode 1 has a further portion 21 secured to it, the portion 21 having an aperture 22 aligned with the aperture 20.

Where the switch is to carry a heavier current the sandwich 3 may be modified as shown in FIGURE 4, to which reference is now made. In this case the layer 6 is replaced by an annular copper ring 23 having an aperture 24 which is arranged to be aligned with the apertures 7 and 8.

The switch may, of course, be used for purposes other than nuclear fusion experiments.

We claim:

1. An electric switch comprising a layer of electricallyinsulating material sandwiched between two expendable electrodes, two main electrodes between which the sandwich is held such that the two main electrodes contact the two expend-able electrodes respectively, the electric in the main electrodes normal to the general plane of the sandwich, a plunger, and means operated when the switch is to be closed to force the plunger into the apertures such that the sandwich is pierced and deformed portions of the expendable electrode first pierced contact the other expendable electrode and complete the electric path between the main electrodes.

2. An electric switch comprising a layer of electricallyinsulating material sandwiched between two metallic layers which form expendable electrodes, two main electrodes between which the sandwich is held such that the two main electrodes contact the two expendable electrodes respectively, the electric supply to be switched being arranged to be connected across the main electrodes, a pair of aligned apertures in the main electrodes normal to the general plane of the sandwich, at plunger, and means operated when the switch is to be closed to force the plunger into the apertures such that the sandwich is pierced and deformed portions of the expendable electrodes are in contact and complete the electric path between the main electrodes.

3. A switch in accordance with claim. 2 wherein the expendable electrode first pierced by the plunger is formed of a relatively soft and ductile metal and the other expendable electrode is formed of a relatively hard metal.

4. A switch in accordance with claim 3 wherein the expendable electrode first pierced by the plunger is formed of soft annealed copper and the other expendable electrode is formed of hard rolled copper.

5. An electric switch comprising a layer of electricallyinsulating material sandwiched between two metallic layers which form expendable electrodes, two main electrodes between which the sandwich is held such that the two main electrodes contact the two expendable electrodes respectively, the electric supply to be switched being arranged to be connected across the main electrodes, a pair of aligned apertures in the main electrodes normal to the general plane of the sandwich, a plunger having at one end a tip portion adapted to enter said apertures and at the other end a disc-like portion the general plane of which is normal to the length of the plunger, a coil situated adjacent said disc-like portion, and means to energise said coil when the switch is to be closed, so that a current of opposite sense to the current in said coil is induced in said disc-like portion and the tip portion of the plunger is forced into the apertures such that the sandwich is pierced and deformed portions of the expendable electrodes are in contact and complete the electric path between the main electrodes.

No references cited.

BERNARD A. GILHEANY, Primary Examiner.

JOSEPH J. BAKER, Assistant Examiner. 

1. AN ELECTIC SWITCH COMPRISING A LAYER OF ELECTRICALLYINSULATING MATERIAL SANDWICHED BETWEEN TWO EXPENDABLE ELECTRODES, TWO MAIN ELECTODES BETWEEN WHICH THE SANDWICH IS HELD SUCH THAT THE TWO MAIN ELECTODES CONTACT THE TWO EXPENDABLE ELECTRODES RESPECTIVELY, THE ELECTRIC SUPLY TO BE SWITCHED BEING ARRANGED TO BE CONNECTED ACROSS THE MAIN ELECTRODES, A PAIR OF ALIGNED APERTURES IN THE MAIN ELECTRODES NORMAL TO THE GENERAL PLANE OF THE SANDWICH, A PLUNGER, AND MEANS OPERATED WHEN THE SWITCH IS TO BE CLOSED TO FORMCE THE PLUNGER INTO THE APERTURES SUCH THAT THE SANDWICH IS PIERCED AND DEFORMED PORTIONS OF THE EXPENDABLE ELECTRODES FIRST PIERCED CONTACT THE OTHER EXPENDABLE ELECTRODE AND COMPLETE THE ELECTRIC PATH BETWEEN THE MAIN ELECTRODES. 